A pillar antenna, roof-mounted antenna, and glass antenna are among the antenna devices that are mounted on a vehicle to support a plurality of frequency bands, or, for example, the antenna devices that support AM and FM bands. However, the pillar antenna, which protrudes greatly, is at high risk of being bent by contact or any other trouble. The roof-mounted antenna needs to be folded or removed in such places as a multistory car park and an automatic car-washing machine because of a higher ground clearance. The problem with the glass antenna is that the antenna involves a specific development for each vehicle model, leading to higher development and production costs and the like. In recent years, great importance has been attached to the design of vehicles. There is growing demand for the vehicle-mounted antenna devices that do not ruin the appearance of vehicles as much as possible. Various antennas that could be built inside a spoiler have been developed so that the appearance is not ruined.
For example, there are such things as a linear monopole antenna element that is disposed from the left end of a vehicle to the right end in space inside a spoiler. Moreover, for example, Japanese Patent Application Kokai Publication No. 2011-035519 discloses an antenna device supporting AM and FM bands, whose antenna is built inside a spoiler. Japanese Patent Application Kokai Publication No. 2008-283609 discloses an example in which a radio or digital TV antenna is disposed in a spoiler.